This research aims to examine the mediating roles of co- creation and employee engagement, as well as the moderating role of authentic leadership, in improving internal service quality within the public sector. Additionally, it explores how internal marketing influences co-creation and employee engagement and their subsequent impact on internal service quality. Utilizing a quantitative research design, data were collected through questionnaires and interviews with 409 civil servants from the Indonesia Provincial Regional Personnel Agency (BKD). SEM analysis using AMOS showed that co-creation mediates the link between internal marketing and employee engagement, and employee engagement mediates the link between internal marketing and internal service quality. Furthermore, authentic leadership moderates the effect of co-creation on employee engagement, indicating that stronger authentic leadership enhances the value of co-creation, thereby improving internal service quality. These findings offer practical insights for the public sector in designing programs that incorporate authentic leadership to enhance service quality, emphasizing the need to improve self-awareness and relational transparency among employees/civil servants. The study contributes to the self-determination theory by integrating it with internal marketing concepts to advance understanding of co-creation, employee engagement, and internal service quality.